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Tropical Storm Douglas Forecast Discussion Number 4
2020-07-21 10:35:45| National Hurricane Center (East Pacific)
Issued at 1100 PM HST Mon Jul 20 2020 000 WTPZ43 KNHC 210835 TCDEP3 Tropical Storm Douglas Discussion Number 4 NWS National Hurricane Center Miami FL EP082020 1100 PM HST Mon Jul 20 2020 Conventional and scatterometer satellite data indicate that Douglas has continued to strengthen, although cloud tops have recently begun to warm. A well-defined CDO, along with a curved convective band in the western semicircle, has developed, and an earlier SSMI/S overpass suggested that a primitive eye feature may be developing. The initial intensity of 50 kt is based on a 0506Z ASCAT-A pass that showed a small area of winds to 45 kt located less than 15 nmi northeast of the center. This intensity is supported by a consensus T3.0/45-kt estimate from TAFB and SAB, and an upward-trending UW-CIMSS ADT intensity estimate of T3.2/49 kt. The symmetrical 34-kt wind radii are based on the aforementioned ASCAT data. The initial motion estimate remains west-southwestward or 255/12 kt. A ridge located between TD-07E to the north and Douglas to the south is expected to keep the latter cyclone moving west-southwestward into Tuesday morning. After that time, the global and regional models are forecasting the ridge to weaken and retreat eastward faster than originally expected, resulting in Douglas turning west-northwestward in 36-48 h. As a result of this more poleward motion, the new NHC official track forecast was shifted north of the previous advisory track, but not as far north as the some of the consensus models and the ECMWF model, which is the northernmost track in the NHC model guidance suite. Although Douglas should remain in a favorable low-shear-high-SST environment for the next 72 h, which would typically favor rapid intensification, the small cyclone will be battling occasional intrusions of dry mid-level air. Such an intrusion appears to be occurring now based on the recent cloud-top warming that has been observed. Thus, only gradual strengthening, with brief periods of arrested development, is expected for the next 3 days. On days 4 and 5, the cyclone will be moving over 25-deg-C SSTs and into an even drier airmass, a negative combination that is expected to induce a slow weakening trend. The new official intensity forecast is similar to the previous advisory, and lies between the consensus models IVCN and NOAA-HCCA. FORECAST POSITIONS AND MAX WINDS INIT 21/0900Z 13.0N 122.8W 50 KT 60 MPH 12H 21/1800Z 12.5N 124.5W 55 KT 65 MPH 24H 22/0600Z 12.2N 127.0W 65 KT 75 MPH 36H 22/1800Z 12.3N 129.7W 75 KT 85 MPH 48H 23/0600Z 13.0N 132.2W 80 KT 90 MPH 60H 23/1800Z 14.2N 134.9W 80 KT 90 MPH 72H 24/0600Z 15.4N 137.6W 75 KT 85 MPH 96H 25/0600Z 17.0N 143.2W 65 KT 75 MPH 120H 26/0600Z 17.8N 148.9W 50 KT 60 MPH $$ Forecaster Stewart
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